Long Term Evolution (LTE) system is based on hybrid automatic repeat request (HARQ) for data transmission. That is, a data receiver selects to return an acknowledgement (ACK) or a negative acknowledgement (NACK) based on whether the data received is correct. Dynamic scheduling of downlink data transmission is achieved through a physical downlink control channel (PDCCH). For semi-persistent scheduling (SPS), initial transmission of SPS data does not need transmission of the PDCCH, but SPS data retransmission needs to be scheduled through the PDCCH.
For an LTE Frequency Division Duplexing (FDD) system, when multiple input-multiple output (MIMO) is adopted for downlink data transmission, two code words (CWs) are generally transmitted in parallel, and a user equipment (UE) will need to feed back two ACK/NACK accordingly. When downlink data is not transmitted via MIMO, only one CW is transmitted, and so the UE will need to feed back only one ACK/NACK accordingly. In contrast, for an LTE TDD (TDD) system, when the number of downlink sub-frames is greater than the number of uplink sub-frames, at least one uplink sub-frame will have to include ACK/NACK for downlink data of multiple downlink sub-frames. In this situation, method A obtains one ACK/NACK bit for each CW by performing a logical and (AND) operation on ACK/NACK for each sub-frame data downlink. However, the downlink data transmission is dynamically scheduled via PDCCH, and the UE may not correctly receive the PDCCH sent by the base station, resulting in different interpretation of the ACK/NACK bit obtained through the above method A between the data sender and the data receiver. To solve this problem, the LTE TDD system adopts downlink allocation indication (DAI) which enables the UE to detect whether the PDCCH in one or more downlink sub-frames is lost during the data transmission. In M downlink sub-frames (where M is an integer larger than or equal to 1) corresponding to an uplink sub-frame, the DAI field in the PDCCH of each downlink sub-frame is used for indicating: up to the current downlink sub-frame, the total number of downlink sub-frames in which PDCCH is sent by the base station, and the value of DAI may be ‘1’, ‘2’, ‘3’, or ‘4’. However, it cannot be detected by utilizing DAI that the last several PDCCH are missed, so the LTE TDD system further requires a UE to return an ACK/NACK in an ACK/NACK channel which is determined by the last sub-frame where a PDCCH is received. Therefore, the base station may determine whether the UE has missed the PDCCH in the last one or multiple sub-frames according to the ACK/NACK channel occupied by the UE. Another method, method B, involves obtaining an ACK/NACK for each sub-frame. If MIMO is adopted for data transmission, an ACK/NACK is obtained by space bundling, and the ACK/NACK composed of multiple bits is transmitted via QPSK modulation in an ACK/NACK channel selected from multiple ACK/NACK channels. In LTE systems, the number of the multiple bits is ‘2’, ‘3’, or ‘4’.
In an enhanced long-term evolution (LTE-A) system, in order to support higher transmission rates, multiple carrier components (CCs) are combined through carrier aggregation (CA) to obtain a larger operating bandwidth. For example, five CCs, each of which has a bandwidth of 20 MHz, can be combined in order to obtain an operating bandwidth of 100 MHz. By adopting CA, the base station is able to transmit downlink data to a UE via multiple CCs, and accordingly, the UE needs to feed back ACK/NACK for the downlink data transmitted via the multiple CCs. Generally, the more accurate the ACK/NACK is, the better the downlink performance will be, but meanwhile the uplink resource overhead and design complexity will be increased accordingly. For an LTE-A TDD system adopting CA, many bits are needed by the UE as the ACK/NACK to be returned. For example, when M equals four and the number of CCs is five, supposing the UE is configured to perform MIMO transmission, the UE needs to return ACK/NACK for forty transmission blocks (TBs) at the most. Specifically, if NACK and DTX(Discontinuity Transmission(TX)) are not distinguished (ACK/NACK is usually divided into three states: ACK—the downlink data is successfully received, NACK—downlink data is detected but received unsuccessfully, DTX—downlink data is not detected), 40-bit ACK/NACK will be fed back; and if NACK and DTX are distinguished, 47-bit ACK/NACK will be fed back. Obviously, so many bits of ACK/NACK being fed back at one time will greatly increase the uplink resource overhead, and will lead to a reduction in uplink coverage. Because the LTE-A uplink control channel of the existing system does not have such a huge feedback volume, a new feedback channel structure needs to be defined to support such a huge bit overhead, which will place higher requirements and increase the complexity and difficulty in implementing the devices.